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How Much Water Went Into Growing the Food We Eat?

The average household purchases a relatively trivial amount of water from their utility, when compared to how much water they purchase in the form of the food they eat. For this reason, reducing residential water consumption will not make much of a difference when it comes to mitigating the effects of a prolonged drought.

To illustrate this point, it is necessary to determine just how much water is available to Californians, and how much of that water is being consumed by residential households in California. When making this analysis, one must not only estimate how much water California’s households purchase from their utility, but how much water is embodied in the food they eat.

TOTAL ANNUAL WATER SUPPLY AND USAGE IN CALIFORNIA

Here’s a rough summary of California’s annual water use. In a dry year, around 150 million acre feet (MAF) fall onto California’s watersheds in the form of rain or snow, in a wet year, we get about twice that much. [1] Most of that water either evaporates, percolates, or eventually runs into the ocean. In terms of net water withdrawals, each year around 31 MAF are diverted for the environment, such as to guarantee fresh water inflow into the delta, 27 MAF are diverted for agriculture, and 6.6 MAF are diverted for urban use. [2] Of the 6.6 MAF that is diverted for urban use, 3.7 MAF is used by residential customers, and the rest is used by industrial, commercial and government customers. [3]

Put another way, we divert 65 million acre feet of water each year in California for environmental, agricultural and urban uses, and the recommended 25% reduction in water usage by residential customers will save exactly 0.9 million acre feet – or 1.4% of our total statewide water usage. One good storm easily dumps ten times as much water onto California’s watersheds as we’ll save via a 25% reduction in annual residential water consumption.

#1 – Total Annual Water Supply and Usage in California

Armed with these facts, there’s a strong argument that cutting back on residential water consumption will not make a significant difference in California’s overall water use. And there are additional facts that can put this argument into an even sharper context: How much water do California’s households consume in terms of the water that was required to grow the food they eat, and how does that amount compare to the water they purchase from their utility for indoor/outdoor use?

THE “WATER FOOTPRINT” OF FOOD PER OUNCE AND PER CALORIE

While the information to determine this is readily available, it isn’t typically compiled in this context, so here goes. The best source of comprehensive data on the “water footprint” for various types of food comes from the Water Footprint Network [4], a project initially funded by UNESCO. An excellent distillation of that information was produced in April 2015 by Kyle Kim, John Schleuss, and Priya Krishnakumar, writing for the Los Angeles Times [5]. Information on calories per ounce was found on the website “fatsecret.com” [6]. That information is summarized on the following table.

#2 – Water “Footprint” per Ounce and per Calorie of Food

As can be seen on the above chart, when evaluating the water efficiency of various food sources, it is misleading to rely only on gallons per ounce, since the number of calories per ounce are highly variable. But putting these two variables together to calculate a gallons per calorie measurement is quite useful. Clearly, meat products require a huge amount of water per calorie. The most efficient sources of meat protein are found in chicken, which at 0.37 gallons per calorie is around four times as water-efficient as red meat. Some sources of protein from vegetables are surprisingly efficient, including avocados at 0.20 gallons per calorie, and the almond – much maligned as a water waster – at 0.15 gallons per calorie. But we digress. How much water does it take to feed the average household in California, and how does that compare to the amount of water they buy from the utility for indoor/outdoor use?

TOTAL ANNUAL CONSUMPTION OF WATER-IN-FOOD PER HOUSEHOLD

The next table, below, provides this estimate based on a typical diet. The estimate of 2,000 calories necessary to sustain the average human (men, women, children) comes from WebMD [7]. The breakout of food consumption by category, while somewhat arbitrary, relies on data on “the average American diet” [8] compiled by researcher Mike Barrett, writing for the Natural Society website. In turn, Barrett relied on USDA and other government sources for most of his data, which is reflected here.

#3 – Total Annual Consumption of Water-in-Food per Household

In one year, the average American consumes a quantity of food that required 1.3 acre feet of water to grow. In turn, at 2.91 people per household in California [9], the average household consumes a quantity of food per year that requires 3.9 acre feet of water to grow.

AVERAGE ANNUAL WATER USE PER CALIFORNIA HOUSEHOLD

Putting all of this together yields a revealing table, below, that shows that the average household purchases a relatively trivial amount of water from their utility, when compared to how much water they purchase in the form of the food they eat. By dividing the 3.7 million acre feet of water used by residences each year in California by the 12.8 million households in California [10], the average annual water consumption per household is 0.289 acre feet. By contrast, the amount of water that is eaten, so to speak, by the average California household is 3.9 acre feet, thirteen and a half times as much. By the way, it is irresistible to point out that drinking water, that quantity each human requires for their daily hydration, based on the 0.5 gallon per day recommendation from AuthorityNutrition.com [11], comes out to a paltry 0.0016 acre feet per year per household – not even a rounding error when compared to the other uses. Think about that the next time you have to ask for your water at a California restaurant.

#4 – Average Annual Water Use per California Household

OBSERVATIONS AND RECOMMENDATIONS

(1) Projects that increase water supply via sewage reuse, runoff storage via reservoirs or aquifers, and desalination, are options that benefit all users, urban and agricultural.

(2) Increasing the supply of water from diverse sources creates system resiliency which can be of critical benefit not only in the face of persistent drought, but also against catastrophes that may, for example, disable a pumping station on a major aqueduct.

(3) The energy costs to desalinate seawater, approximately 4.0 kilowatt-hours per cubic meter, are overstated. Desalination plants can be co-located with power plants, eliminating power loss through transmission lines, whereas far-flung pumping stations consume significant amounts of electricity. Depending on transmission loss and desalination plant efficiency, the amount of lift beyond which desalination consumes less power than pumping is about 1,500 feet.

(4) Public investment in water saving home appliances, for example via tax rebates to consumers to purchase them, by contrast, do not increase the overall supply of water.

(5) It is nearly impossible to engage in excessive use of indoor water in a household, because 100% of the sewage is treated and released as clean outfall to the environment. Moreover, sewage is increasingly treated and reused as potable water, and eventually 100% of indoor water waste will be cycled immediately back for reuse by households.

(6) One preferred way to reuse household sewage is referred to as “indirect potable reuse,” where the treated water is percolated into aquifers where it is eventually pumped back for household reuse. This practice has the virtue of banking the water against supply disruptions, recharging the aquifer which is especially beneficial in coastal areas where there can be salt water intrusion, and even, as water is repeatedly cycled through the aquifer, causing an ongoing improvement to the quality of the water in the aquifer as treatment progressively reduces levels of undesirable residual toxins.

(7) While achieving 100% reuse of sewage will render indoor water conservation pointless, the virtues of outdoor water use are understated. Healthy landscaping, consisting of abundant vegetation including lawns, reduce the incidence of dust-borne pathogens, reduce the incidence of asthma, and clean and moisturize the air. Replacing grass playing fields with artificial turf introduces toxins, causes more ACL and other sports injuries, and retains heat – often to the point of making these faux fields unplayable unless they are, ironically, watered.

(8) Simply giving up consumption of red meat would reduce the average household’s water consumption by nearly 2.0 acre feet per year. By comparison, the average Californian household’s total water consumption from the utility averages 0.29 acre feet per year. That is, just replacing consumption of red meat with an equivalent caloric intake of chicken will save the average household seven times as much water as they buy from the utility for all uses, indoor and outdoor.

Policies designed to reduce household water use are a good idea, but must be kept in perspective. Perhaps what has already been done is more than enough, and priorities might now shift towards investment in infrastructure to increase the supply of water. Nearly all water diversions in California, about 90%, are either to preserve ecosystem health or to supply agriculture. Indoor water overuse is becoming a myth, and will become entirely irrelevant as soon as 100% sewage reuse capacities are achieved. Outdoor water use should not be thoughtless, but allowing grass and perennials to die, or converting landscaping to “desert foliage,” is a cultural shift that is not necessary or desirable.

Along with investing in infrastructure to increase the supply of water, public education to help Californians adopt healthier diets would have the significant side benefit of being sound water policy. A trivial change in patterns of food consumption yields a major reduction in water required for food. For example, a public education campaign that caused a voluntary 10% reduction in red meat consumption (from 25.0% of all calories to 22.5% of all calories) would reduce California’s water consumption by 2.5 million acre feet per year. By comparison, total outdoor residential water consumption in California is estimated at only 1.8 million acre feet per year.

Perhaps, in lieu of renouncing escalating and entirely unnecessary mandates to reduce household water use, those of us who love our lawns might at least be granted a waiver if we were to present an annual affidavit to document our below-average consumption of red meat. Our smart refrigerators might actually submit the report to the utility, sparing us the paperwork.